Voltage level shifting circuits are well-known in the art. Typically, they are classified either as shift-up or shift-down circuits. They receive an input signal which varies between a first voltage and a second voltage. They produce an output signal which varies between a first voltage and a third voltage. In a shift-up circuit the third voltage of the output signal is greater than the second voltage of the input signal. In a shift-down circuit, the opposite is true.
In many types of digital signal application, it is desired to have a voltage level greater than the common digital signal, which varies between zero volts and 5 volts. For example, to program a EEPROM memory device, it is desired to have a voltage level varying between zero volts and a high voltage level, such as .degree.volts. Thus, voltage level shifting circuits of the shift-up types are required.
Voltage level shifting circuits have been described in the literature. See, for example, U.S. Pat. Nos. 4,132,904; 4,418,293; 4,580,245; 4,375,677; 4,342,101; 4,460,978; 4,131,951; and 4,542,484. Although none of the foregoing references teaches or suggests applicants's invention, the closest reference appears to be U.S. Pat. No. 4,132,904 in FIG. 7 thereof. However, applicant believes that the invention, as set forth herein, has many advantages over the voltage level shifting circuits of the prior art.